This invention relates generally to hydraulic shock absorber devices. More particularly, this invention relates to a new and improved shock absorber employed in the suspension system of a motorcycle or other vehicle.
A well-recognized problem associated with hydraulic shock absorbers employing a damping piston which reciprocates in a cylinder filled with a damping fluid are the temperature dependent damping characteristics of the shock absorber. Generally an increase in the temperature of the damping fluid decreases the viscosity of the fluid and adversely effects the damping characteristics of the shock absorber. When a vehicle travels over a rough terrain under intense operational conditions such as may occur during motocross racing, the rapid reciprocative axial movement of the damping piston causes the temperature of the damping fluid to rise rapidly. The temperature increase to the damping fluid is exacerbated when the ambient temperature is relatively high and the vehicle is being operated at relatively high speeds. Under such conditions, the viscosity of the damping fluid may decrease to a very low level wherein the damping characteristics of the damping piston may be greatly diminished resulting in a significant lessening of the vehicle stability and ultimately jeopardizing the driveability of the vehicle.
A number of devices and techniques have been advanced to eliminate or compensate for the adverse temperature dependant operational characteristics normally inherent in a hydraulic shock absorber. In U.S. Pat. No. 2,785,774 an outer sleeve is positioned within a shock absorber cylinder to divide the hydraulic fluid chamber into two chambers. The hydraulic fluid is cooled by causing a uni-directional flow of the hydraulic fluid into the chambers for continuously removing heat from the fluid. U.S. Pat. No. 4,337,849 discloses a modification to a conventional shock absorber by adding an additional cylinder concentric with the shock absorber to form an annular reservoir around the shock absorber. Temperature sensitive valves are employed to release heated oil from the damping chamber to the reservoir for cooling the oil. In U.S. Pat. No. 3,795,291 a shock absorber for a motorcycle employs an outer casing which constitutes a fluid storage chamber. The fluid storage chamber connects to a cooling device for cooling hydraulic fluid in the chamber. The cooling device includes cooling fins for dissipating the heat with the damping fluid being circulated to the cooling device.